液体ヘリウム中の浸漬冷却超電導導体に生じる熱擾乱とクエンチの光学的観測

抄録

The present authors have succeeded in optical observation on thermal disturbance, quench zone, and its rapid propagation in a superconducting coil, immersion-cooled in liquid helium, by producing the respective dark zones corresponding to them on its illuminated surface. The thermal disturbance to the test coil was applied by pulse-heating of film heaters wound in it. Transient behavior of the dark zones under various conditions of pulse heating and transport current was recorded with a high-speed video system, and compared with the measured time histories of tap voltages and temperatures at various locations of the test coil; the agreement was very good. Fundamental study by experiments using a pulse-heated strip of stainless steel film revealed the following: The optical observation is possible when the wall heat flux of the test piece is greater than 140W/m² and its wall superheat is greater than 0.3K. In such a case, a light beam is scattered in a very thin thermal layer at the liquid-solid interface and luminous energy of reflected light from the interface is attenuated. With increasing pulse-heat flux, the reflected luminous energy decreases drastically and initiation time of the attenuation is shortened.